Why does The First Berserker: Khazan FPS drop after one match?

It's so annoying; even though CPU usage wasn't high, by the second match, the frame rate would drop from 110 to 60. I tried opening the chassis side panel, which dropped the temperature by 4℃, but the frame drops still returned after half an hour; this temporary fix was a joke. I used the GamePP Fan Curve Configuration Panel to set the CPU fan to 100% at 70℃ and used the BIOS Load-Line Voltage Guide to set LLV to L2 mode to reduce power and heat. CPU temperature was suppressed to 78-84℃ per AIDA64, and core voltage stabilized at 1.18-1.22V per GamePP.